Patent GB-134585-A (GB)
IPC: H03C1/10
Abstract: 134,585. British Thomson - Houston Co., (General Electric Co.). Oct. 4, 1918. Wireless signalling; electric oscillations, producing.-In order to minimize the effect of static disturbances on the receiving-instruments, amplitude pulses of an inaudible frequency are produced either by the generation in the transmitting-aerial of oscillations of two frequencies (say 75,000 and 80,000), or by applying the second frequency to the receiving-system from a local source. The currents of inaudible frequency are accumulated in a resonant circuit at the receiving-station, and are detected by heterodyning from a low-frequency generator, or otherwise. Transmitting-systems. In the transmitting- system shown in Fig. 1, an alternator 1 of radio frequency supplies energy to the aerial through a transformer 3 the secondary of which is earthed at its mid-point. The halves of the secondary winding communicate with the aeral through the magnetic controllers 4, 5, which a.re of the type described in Specification 103,842. The inductance of the reactive windings 6, 7 is varied by the controlling-windings 10, 11. The windings 10 receive direct current from a generator 13, and, when the signalling-key 20 is depressed, the windings 11 receive alternating current from the alternator 12, at a frequency of, say, 5000. The windings 10, 11 are so arranged that, during a half-cycle in which the reactance of the windings 6, 7 of the controller 4 becomes a minimum by the conjoint action of the direct and alternating currents in the coils 10, 11 and consequent saturation of the iron, the currents in the coils 10, 11 of the controller 5 will oppose one another, and the reactance of the windings 6, 7 will become a maximum. By means of the inductance 14 and the combined inductance and capacity 16, 15, the aerial is doubly tuned. If the frequency of the alternator 1 is 75,000 and that of the alternator 12 is 5000, the tunings of the aerial may be 80,000 and 75,000. The result may be regarded as a high-frequency radiation with amplitude pulses at a frequency of 5000. To enable the alternator 1 to deliver full power continuously, a storage circuit may be made up of the condenser 19 and the primary of the transformer 3. In a modification, one magnetic controller alone is used, having a single controlling- winding supplied from the alternator 12 in series with a battery having a potential substantially equal to its own, so that, in alternate half-cycles, the current in the controlling-winding falls to zero. In another modification, the loop circuit which provides the second tuning for the aerial serves also as the storage circuit, being inductively coupled, for that purpose, with the reactance circuit of one of the magnetic controllers, so that when this controller is non-inductive, energy flows into the storage circuit, while, when the other controller is non-inductive, the energy flows directly into the aerial. Receiving-systems. Fig. 5 shows a receiving- system with doubly tuned aerial. The amplifier 36 magnifies the pulsations at the inaudible forequency, and they pass by the transformer 41 to a resonant circuit 43, 44, where they act accumulatively. To make the signals audible, a local source 45 of alternating current of slightly different frequency from that of the current in the circuit 42 is introduced into the grid circuit of the amplifier 46. An aperiodic or strongly damped aerial may be used instead of the doubly tuned aerial shown in Fig. 5. Fig. 6 shows a receiving- system differing from Fig. 5 in two respects. In tne first place, it is adapted to receive waves at a single radio-frequency, the amplitude pulses of inaudible frequency being produced by beats with a local high-frequency generator 63. Secondly, the circuit 43, 44 is partly screened from the effects of static disturbances by the interposition of a double-iron cored transformer 55, 56 with a regulating-winding 57 which receives current from a battery 58. This transformer limits the voltage that can be transmitted to the circuit 43, 44, as excessive shocks by statics bring about saturation of the iron. In a modification, a magnetic controller of the kind shown in Fig. 1 is inserted in the plate circuit of the amplifier 36, the direct current in its control winding being so adjusted that an increase of current in its reactance windings brings the inductance closer to perfect tuning for the pulses of inaudible frequency to be passed to the circuit 43, 44. A progressive change of current and inductance thus takes place and the oscillations of inaudible frequency build up to a maximum. If currents produced by strays and of greater magnitude than the signal currents act upon this inductance, they tend to change the tuning beyond the point of maximum sensitiveness and produce but slight increase on the cutrent flowing in the circuit. Specifications 16443/15 and 102.503 also are referred tn.